This invention relates generally to avalanche photodiodes and, more particularly, to an avalanche photodiode (APD) for use in harsh environments, such as oil well drilling applications, wherein the avalanche photodiode comprises silicon carbide (SiC) materials or gallium nitride (GaN) materials.
There is currently a need for gamma ray detection in the oil well drilling industry. High energy gamma rays reflected from Hydrogen (H) bearing compounds underground may indicate specific locations which may have oil. A small, robust sensor capable of detecting such rays is highly desirable and necessary for harsh, down-hole environments where shock levels are near 250 gravitational acceleration (G) and temperatures approach or exceed 150° Celsius (C).
Several current technologies utilize photomultiplier tubes (PMTs) to transform low-level ultraviolet (UV) light signals to readable level electronic signals. However, PMTs have a negative temperature coefficient. Thus, PMTs become less sensitive as temperature increases. PMTs are also fragile and prone to fail when vibration levels are high. For certain applications (e.g., at 150° C. where PMTs have ˜50% signal), the lifetimes of PMTs may become prohibitively short, thereby driving the cost of their use up sharply. Another problem faced by PMTs involves high noise levels, which make accurate signal detection increasingly difficult.
APDs are high-speed, high sensitivity photodiodes utilizing an internal gain mechanism that functions by applying a reverse voltage. Compared to PIN photodiodes, APDs can measure even lower level light and are used in a wide variety of applications requiring high sensitivity. Silicon may be used in APDs due to its very high ionization coefficient ratio, which results in a high-gain bandwidth product and very low excess noise. However, silicon has a very low absorption coefficient especially at a fiber-optic and free-space optical communications wavelengths at 1.3 microns and 1.5 microns. An advantage of using silicon for a multiplication region within an ADP is due to a high ionization coefficient ratio, which results in much higher sensitivity, higher-gain bandwidth product, lower noise and higher temperature and voltage stability.
Other conventional APDs may include near-infrared indium gallium arsenide/indium phosphide (InGaAs/InP) APDs that are limited in performance by a small ionization coefficient ratio, which results in low-gain bandwidth product and high excess noise. At shorter wavelengths, silicon (Si) APDs are used extensively for applications where high sensitivity and high-gain bandwidth product are required.
Conversely, silicon is likely not to perform well at high temperatures and high vibration environments. Silicon has inherent disadvantages which preclude its ease of use and implementation in many applications. More specifically, Si-based devices suffer largely from degradation when exposed to harsh environments or temperatures above 150 degrees Celsius. Complex, expensive cooling systems and packages are required to facilitate successful operation of Si-based APDs, limiting their wide spread use in harsh environment applications.
These and other drawbacks exist in current systems and techniques.